Tire

ABSTRACT

A tire includes a first middle land portion having circumferentially extending first and second longitudinal edges. The first middle land portion is provided with middle lateral grooves. At least one of the middle lateral grooves includes a first groove portion extending in the tire axial direction from the first longitudinal edge, and a second groove portion extending in the tire axial direction from the second longitudinal edge. The first groove portion and the second groove portion are offset in the tire circumferential direction to form a pair of circumferential groove edges between a pair of groove edges of the first groove portion and a pair of groove edges of the second groove portion. A maximum groove depth of the first groove portion is different from a maximum groove depth of the second groove portion.

RELATED APPLICATIONS

This application claims the benefit of foreign priority to JapanesePatent Application No. JP2022-027770, filed Feb. 25, 2022, which areincorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a tire.

BACKGROUND OF THE DISCLOSURE

Patent Document 1 below has proposed a tire that includes middle landportions provided with a plurality of middle lateral grooves. The middlelateral grooves are provided with tie-bars in which groove bottoms raiselocally. The tire is expected to improve on-snow performance whilemaintaining stability on dry roads.

PATENT DOCUMENT

-   [Patent document 1] Japanese Unexamined Patent Application    Publication 2015-168356

SUMMARY OF THE DISCLOSURE

In recent years, as the performance of power units of vehicles hasimproved, there has been a demand for further improvements in terms ofon-snow performance while maintaining steering stability on dry roads.

The present disclosure has been made in view of the above circumstancesand has a main object to provide a tire capable of exerting excellenton-snow performance while maintaining steering stability on dry roads.

In one aspect of the present disclosure, a tire includes a tread portionincluding a first tread edge, a second tread edge, a first middle landportion arranged between the first tread edge and the second tread edge.The first middle land portion includes a first longitudinal edgeextending in a tire circumferential direction on a first tread edgeside, a second longitudinal edge extending in the tire circumferentialdirection on a second tread edge side, and a ground contact surfacebetween the first longitudinal edge and the second longitudinal edge.The first middle land portion is provided with a plurality of middlelateral grooves that traverses the first middle land portion completelyin a tire axial direction. At least one of the plurality of middlelateral grooves includes a first groove portion extending in the tireaxial direction from the first longitudinal edge, and a second grooveportion extending in the tire axial direction from the secondlongitudinal edge. The first groove portion and the second grooveportion are offset in the tire circumferential direction to form a pairof circumferential groove edges extending in the tire circumferentialdirection between a pair of groove edges of the first groove portion anda pair of groove edges of the second groove portion. A maximum groovedepth of the first groove portion is different from a maximum groovedepth of the second groove portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a development view of a tread portion showing an embodiment ofthe present disclosure;

FIG. 2 is an enlarged view of a first middle land portion of FIG. 1 ;

FIG. 3 is an enlarged view of a first middle lateral groove and a secondmiddle lateral groove;

FIG. 4 is a cross-sectional view taken along the line A-A of FIG. 2 ;

FIG. 5 is a cross-sectional view taken along the line B-B of FIG. 2 ;

FIG. 6 is a cross-sectional view taken along the line C-C of FIG. 2 ;

FIG. 7 is a cross-sectional view taken along the line D-D of FIG. 2 ;

FIG. 8 is a cross-sectional view taken along the line E-E of FIG. 2 ;

FIG. 9 is an enlarged view of a crown land portion of FIG. 1 ;

FIG. 10 is an enlarged view of a first crown sipe, a second crown sipe,a third crown sipe and a fourth crown sipe of FIG. 9 ;

FIG. 11 is an enlarged view of a second middle land portion of FIG. 1 ;

FIG. 12 is a cross-sectional view taken along the line F-F of FIG. 11 ;

FIG. 13 is a cross-sectional view taken along the line G-G of FIG. 11 ;and

FIG. 14 is an enlarged view of the second middle land portion inaccordance with another embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

One or more embodiments of the present disclosure will be describedbelow with reference to the drawings.

FIG. 1 is a development view of a tread portion 2 of a tire 1 showing anembodiment of the present disclosure. The tire 1 according to thepresent embodiment, for example, is embodied as a winter tire and may besuitably used as a pneumatic tire for passenger cars. However, thepresent disclosure is not limited to such an embodiment, and may beapplied to heavy-duty pneumatic tires and non-pneumatic tires in whichthe interior of the tire is not filled with pressurized air.

As illustrated in FIG. 1 , the tread portion 2 according to the presentdisclosure includes a first tread edge T1, a second tread edge T2, aplurality of circumferential grooves 3 extending continuously in thetire circumferential direction between the first tread edge T1 and thesecond tread edge T2, and a plurality of land portions 4 divided by thecircumferential grooves 3. As a preferred embodiment, the tire 1according to the present embodiment is configured as a so-calledfive-rib tire in which the tread portion 2 is composed of fourcircumferential grooves 3 and five land portions 4.

In the present embodiment, the tread portion 2, for example, has adesignated mounting direction on a vehicle. Thus, the first tread edgeT1 is intended to be positioned outside the vehicle when installed, andthe second tread edge T2 is intended to be positioned inside the vehiclewhen installed. The mounting direction on a vehicle is indicated, forexample, by letters or symbols on a sidewall portion (not illustrated)of the tire 1. However, the tire 1 according to the present disclosureis not limited to such an embodiment and may be used without specifyingthe mounting direction on a vehicle.

The first tread edge T1 and the second tread edge T2 are the axialoutermost edges of the ground contacting patch of the tire 1 whichoccurs under the condition such that the tire 1 under a normal state isgrounded on a plane by zero camber angles with 70% of a standard tireload.

As used herein, when a tire is a pneumatic tire based on a standard, the“normal state” is such that the tire 1 is mounted onto a standard wheelrim with a standard pressure but loaded with no tire load. If a tire isnot based on the standards, or if a tire is a non-pneumatic tire, thenormal state is a standard state of use according to the purpose of useof the tire and means a state of no load. As used herein, unlessotherwise noted, the dimensions of portions of the tire are valuesmeasured under the normal state.

As used herein, the “standard wheel rim” is a wheel rim officiallyapproved for each tire by standards organizations on which the tire isbased, wherein the standard wheel rim is the “standard rim” specified inJATMA, the “Design Rim” in TRA, and the “Measuring Rim” in ETRTO, forexample.

As used herein, the “standard pressure” is a standard pressureofficially approved for each tire by standards organizations on whichthe tire is based, wherein the standard pressure is the “maximum airpressure” in JATMA, the maximum pressure given in the “Tire Load Limitsat Various Cold Inflation Pressures” table in TRA, and the “InflationPressure” in ETRTO, for example.

As used herein, when a tire is a pneumatic tire based on a standard, the“standard tire load” is a tire load officially approved for each tire bythe standards organization in which the tire is based, wherein thestandard tire load is the “maximum load capacity” in JATMA, the maximumvalue given in the above-mentioned table in TRA, and the “Load Capacity”in ETRTO, for example. Also, in the case of tires for which variousstandards are not specified, “standard tire load” refers to the maximumload that can be applied when using the tire according to theabove-mentioned standards.

The circumferential grooves 3 include a first shoulder circumferentialgroove 5 and a second shoulder circumferential groove 6. Further, thecircumferential grooves 3 include a first crown circumferential groove 7and a second crown circumferential groove 8, which are arranged betweenthe first and second shoulder circumferential grooves 5 and 6. The firstshoulder circumferential groove 5 is located nearest to the first treadedge T1 among the circumferential grooves 3. The second shouldercircumferential groove 6 is located nearest to the second tread edge T2among the circumferential grooves 3. The first crown circumferentialgroove 7 is located between the first shoulder circumferential groove 5and the tire equator C. The second crown circumferential groove 8 islocated between the second shoulder circumferential groove 6 and thetire equator C.

Preferably, a distance L1 in the tire axial direction from the tireequator C to the groove centerline of the first shoulder circumferentialgroove 5 or the second shoulder circumferential groove 6 is, forexample, in a range from 25% to 35% of the tread width TW. Preferably, adistance L2 in the tire axial direction from the tire equator C to thegroove centerline of the first crown circumferential groove 7 or thesecond crown circumferential groove 8 is, for example, in a range from5% to 15% of the tread width TW. Note that the tread width TW is thedistance from the first tread edge T1 to the second tread edge T2 in thetire axial direction under the normal state.

In the present embodiment, the second shoulder circumferential groove 6,the first crown circumferential groove 7, and the second crowncircumferential groove 8 each extend in a straight manner in parallelwith the tire circumferential direction. On the other hand, the firstshoulder circumferential groove 5 has a zigzag groove edge on the tireequator C side. However, each of the circumferential grooves 3 is notlimited to such a shape.

The circumferential grooves 3 have a groove width W1 which is preferablyequal to or more than 3 mm. In addition, the groove width W1 of thecircumferential grooves 3, for example, is preferably in a range from3.0% to 7.0% of the tread width TW. A groove depth of thecircumferential grooves 3 is in a range from 5 to 10 mm for passengercar tires, for example.

The land portions 4 according to the present embodiment include a firstmiddle land portion 13 located between the first tread edge T1 and thesecond tread edge T2. In some preferred embodiments, the first middleland portion 13 is located between the first tread edge T1 and the tireequator C and is specifically sectioned between the first shouldercircumferential groove 5 and the first crown circumferential groove 7.Further, the land portions 4 according to the present embodiment includea first shoulder land portion 11, a second shoulder land portion 12, asecond middle land portion 14 and a crown land portion 15. The firstshoulder land portion 11 includes the first tread edge T1 and isadjacent to the first middle land portion 13 via the first shouldercircumferential groove 5. The second shoulder land portion 12 includesthe second tread edge T2 and is located outwardly in the tire axialdirection of the second shoulder circumferential groove 6. The secondmiddle land portion 14 is located between the second tread edge Te andthe tire equator C, and specifically is sectioned between the secondshoulder circumferential groove 6 and the second crown circumferentialgroove 8. The crown land portion 15 is sectioned between the first crowncircumferential groove 7 and the second crown circumferential groove 8and thus is located on the tire equator C.

FIG. 2 illustrates an enlarged view of the first middle land portion 13.As illustrated in FIG. 2 , the first middle land portion 13 includes afirst longitudinal edge 13 a extending in the tire circumferentialdirection on the first tread edge T1 side, a second longitudinal edge 13b extending in the tire circumferential direction on the second treadedge T2 side, and a ground contact surface 13 s between the firstlongitudinal edge 13 a and the second longitudinal edge 13 b. Inaddition, the first middle land portion 13 is provided with a pluralityof middle lateral grooves 20.

FIG. 3 illustrates an enlarged view of two middle lateral grooves 20.Note that FIG. 3 is an enlarged view of a first middle lateral groove 21and a second middle lateral groove 22 which will be described later. Asillustrated in FIG. 3 , at least one of the middle lateral grooves 20includes a first groove portion 26 and a second groove portion 27. Thefirst groove portion 26 extends from the first longitudinal edge 13 a inthe tire axial direction. The second groove portion 27 extends from thesecond longitudinal edge 13 b in the tire axial direction.

In the present disclosure, the first groove portion 26 and the secondgroove portion 26 are offset in the tire circumferential direction toform a pair of circumferential groove edges 28 e extending in the tirecircumferential direction between a pair of groove edges 26 e of thefirst groove portion 26 and a pair of groove edges 27 e of the secondgroove portion 27. In addition, the maximum groove depth of the firstgroove portion 26 is different from the maximum groove depth of thesecond groove portion 27. The tire in accordance with the presentdisclosure, by adopting the above-mentioned structure, can exertexcellent on-snow performance while maintaining steering stability ondry roads (hereinafter, it may be simply referred to as “steeringstability”). The reason for this is presumed to be the followingmechanism.

When driving on snow, the middle lateral grooves 20 can compress snowinside the grooves and shear it, thereby providing a large reactionforce (such reaction force may be sometimes referred to as “snow columnshearing force”). Since the maximum groove depths of the first grooveportion 26 and the second groove portion 27 are different from eachother, the groove with the smaller maximum depth can maintain therigidity of the first middle land portion 13 and thus the steeringstability can be maintained. On the other hand, the groove with thegreater maximum groove depth can provide a larger snow column shearingforce, which can improve on-snow performance.

In addition, the pair of circumferential groove edges 28 e describedabove can provide frictional force in the tire axial direction and helpto improve cornering performance on snow. Furthermore, the combinationof the circumferential groove edges 28 e, the first groove portion 26,and the second groove portion 27 described above can compress the snowentering the groove with the greater maximum depth more strongly in thetire axial direction to generate a powerful snow column shearing force.It is considered that the tire 1 according to the present disclosure canexert excellent on-snow performance while maintaining the steeringstability by such a mechanism.

Hereinafter, a more detailed configuration of the present embodimentwill be described. Note that each configuration described below shows aspecific aspect of the present embodiment. Thus, the present disclosurecan exert the above-mentioned effects even if the tire does not includethe configuration described below. Further, if any one of theconfigurations described below is applied independently to the tire ofthe present disclosure having the above-mentioned characteristics, theperformance improvement according to each additional configuration canbe expected. Furthermore, when some of the configurations describedbelow are applied in combination, improvements of the respectiveperformance based on the additional configuration can be expected.

As illustrated in FIG. 2 and FIG. 3 , in the present embodiment, each ofthe middle lateral grooves 20 has the above-mentioned structure. In atread plan view. the first groove portions 26 and the second grooveportions 27 extend in the tire axial direction with a constant groovewidth W3 (shown in FIG. 2 ). The groove width W3 of the first grooveportions 26 and the second groove portions 27, for example, ranges from15% to 25% of a width W2 (shown in FIG. 2 ) in the tire axial directionof the ground contact surface 13 s of the first middle land portion 13.An angle of the first groove portions 26 and the second groove portions27 ranges from 25 to 35 degrees with respect to the tire axialdirection, for example.

The middle lateral grooves 20 include a plurality of first middlelateral grooves 21 and a plurality of second middle lateral grooves 22which have different distribution of groove depths from each other. Thefirst middle lateral grooves 21 and the second middle lateral grooves 22are arranged alternately in the tire circumferential direction.

FIG. 4 illustrates a cross-sectional view taken along the line A-A ofFIG. 2 . FIG. 4 is a cross-sectional view of one of the first middlelateral grooves 21 along a groove longitudinal direction thereof. FIG. 5illustrates a cross-sectional view taken along the line B-B of FIG. 2 .FIG. 5 is a cross-sectional view of one of the second middle lateralgrooves 22 along a groove longitudinal direction thereof. As illustratedin FIG. 4 and FIG. 5 , in the present embodiment, the first grooveportions 26 and the second groove portions 27 of the first middlelateral grooves 21 and the first groove portions 26 and the secondgroove portions 27 of the second middle lateral grooves 22 extend in thegroove longitudinal direction with respective constant groove depths.

As illustrated in FIG. 4 , in each first middle lateral groove 21, themaximum groove depth d1 of the first groove portion 26 is smaller thanthe maximum groove depth d2 of the second groove portion 27. In each ofthe first middle lateral grooves 21, the groove depth d2 of the secondgroove portion 27, for example, ranges from 60% to 80% of a groove depthdc of the first crown circumferential groove 7. Further, in each of thefirst middle lateral grooves 21, the groove depth d1 of the first grooveportion 26 ranges from 40% to 60% of the groove depth dc of the firstcrown circumferential groove 7. Preferably, the groove depth d1 of thefirst groove portion 26 ranges from 60% to 70% of the groove depth d2 ofthe second groove portion 27.

As illustrated in FIG. 5 , the second middle lateral groove 22 hassubstantially the inverted shape of the first middle lateral groove 21.That is, in each of the second middle lateral grooves 22, the maximumgroove depth d1 of the first groove portion 26 is greater than themaximum groove depth d2 of the second groove portion 27. In each of thesecond middle lateral grooves 22, the groove depth d1 of the firstgroove portion 26, for example, ranges from 60% to 80% of the groovedepth dc of the first crown circumferential groove 7. Further, in eachof the second middle lateral grooves 22, the groove depth d2 of thesecond groove portion 27 ranges from 40% to 60% of the groove depth dcof the first crown circumferential groove 7. Preferably, the groovedepth d2 of the second groove portion 27 ranges from 60% to 70% of thegroove depth d1 of the first groove portion 26.

In the present embodiment, since the first middle lateral grooves 21 andthe second middle lateral grooves 22 are provided alternately in thetire circumferential direction, the steering stability and on-snowperformance can be improved in a well-balanced manner.

FIG. 6 illustrates a cross-sectional view taken along the line C-C ofFIG. 2 . FIG. 6 is a cross-sectional view of the second groove portion27 of each of the first middle lateral grooves 21, or the first grooveportion 26 of each of the second middle lateral grooves 22 (hereinafter,sometimes referred to collectively as deep groove portion 37). FIG. 7illustrates a cross-sectional view take along the line D-D of FIG. 2 .FIG. 7 is a cross-sectional view of the first groove portion 26 of eachof the first middle lateral grooves 21, or the second groove portion 27of each of the second middle lateral grooves 22 (hereinafter, sometimesreferred to collectively as shallow groove portion 36).

As illustrated in FIG. 6 and FIG. 7 , the deep groove portion 37 and theshallow groove portion 36 preferably open at the ground contact surfacevia chamfer portions 25. Each chamfer portion 25 includes an inclinedsurface 25 s between the ground contact surface 13 s and one of thegroove walls. In the present embodiment, each inclined surface 25 s isslightly curved in a direction convex outward in the tire radialdirection. The inclined surface 25 s may, for example, be planar. Such achamfer portion 25 can help to equalize the ground pressure acting onthe ground contact surface 13 s to improve uneven wear resistance.

As illustrated in FIG. 6 , the deep groove portion 37, for example, isconfigured to include a flat groove bottom 37 d. On the other hand, asillustrated in FIG. 7 , the shallow groove portion 36 includes a groovebottom 36 d which is provided with a groove bottom sipe 38 extendinginwardly in the tire radial direction. The definition of “sipe” will bediscussed later. Such a groove bottom sipe 38 can facilitate the openingof the shallow groove portion 36 appropriately and help to improveon-snow performance. Note that the above-mentioned depths d1 and d2 ofthe first groove portion 26 of each first middle lateral groove 21 andthe second groove portion 27 of each second middle lateral groove 22,respectively, mean a depth excluding the groove bottom sipe 38. Inaddition, in FIG. 4 and FIG. 5 , the groove bottom sipes 38 are notillustrated. In some preferred embodiments, a total depth from theground contact surface 13 s to a bottom of the groove bottom sipe 38 isalso smaller than a depth of the deep groove portion 37. This canimprove the balance between steering stability and on-snow performance.

In the present embodiment as illustrated in FIG. 3 , each of the pair ofgroove edges of each middle lateral groove 20 includes a respective oneof the pair of circumferential groove edges 28 e. The pair ofcircumferential groove edges 28 e, for example, is located in thecentral area when the ground contact surface 13 s of the first middleland portion 13 is divided into three equal portions in the tire axialdirection. In the present embodiment, the pair of circumferential grooveedges 28 e is positioned such that the axial center position of theground contact surface 13 s of the first middle land portion 13 islocated therebetween. In addition, the pair of circumferential grooveedges 28 e extends along the tire circumferential direction, preferablyextending in parallel with the tire circumferential direction. Forexample, an angle of the pair of circumferential groove edges 28 e ispreferably equal to or less than 10 degrees, more preferably equal to orless than 5 degrees with respect to the tire circumferential direction.Preferably, a length L3 in the tire circumferential direction of eachcircumferential groove edge 28 e is smaller than the maximum width ofthe first groove portion 26 and the second groove portion 27.Specifically, the length L3 ranges from 75% to 95% of the maximum groovewidth. Such a circumferential groove edge 28 e can improve corneringperformance when driving on snow, while suppressing uneven wear of theland portion.

Each middle lateral groove includes a circumferential groove portion 28located between the first groove portion 26 and the second grooveportion 27. In the present embodiment, the area between one of the pairof circumferential groove edge 28 e and its imaginary extension lineextending in a longitudinal direction thereof and the other one of thepair of circumferential groove edge 28 e and its imaginary extensionline extending in a longitudinal direction thereof is configured as thecircumferential groove portion 28.

As illustrated in FIG. 4 and FIG. 5 , the maximum groove depth d3 of thecircumferential groove portions 28 is smaller than the maximum groovedepth d1 of the first groove portions 26 and the maximum groove depth d2of the second groove portions 27. Specifically, the maximum groove depthd3 of the circumferential groove portions 28 ranges from 20% to 30% ofthe groove depth dc of the first crown circumferential groove 7. Thecircumferential groove portions 28 can increase the rigidity of a middleregion of the first middle land portion 13 and improve uneven wearresistance.

As illustrated in FIG. 2 , it is preferable that the first middle landportion 13 is provided with at least one circumferential sipe 30extending in the tire circumferential direction. In the presentembodiment, the first middle land portion 13 is provided with aplurality of circumferential sipes 30 spaced in the tire circumferentialdirection.

As used herein, “sipe” means a groove-shaped body (a recess having alongitudinal direction, including grooves) having a small width andincludes a main body portion thereof having a width between two oppositeinner walls being 1.5 mm or less. Further, the main body portion means aportion in which two opposite inner walls extend parallel orsubstantially parallel to each other in the tire radial direction. Here,“substantially parallel” means that the angle between two opposite innerwalls is 10 degrees or less. As will be described later, sipe may beprovided with one or more chamfer portions. Further, sipe may have aso-called flask bottom with an increased width at the bottom. Note thatin the present embodiment, the circumferential sipes 30 extend in thetire radial direction from the ground contact surface 13 s to respectivebottoms thereof with a constant width.

Preferably, each circumferential sipe 30, for example, is located in thecentral area when the ground contact surface 13 s of the first middleland portion 13 is divided into three equal portions in the tire axialdirection. An angle of each circumferential sipe 30 with respect to thetire circumferential direction is, for example, equal to or less than 10degrees, preferably equal to or less than 5 degrees. Such acircumferential sipe 30 can provide a large frictional force in the tireaxial direction when driving on snow.

Each of the circumferential sipes 30, for example, extends across arespective one of the middle lateral grooves 20 in the tirecircumferential direction. In some preferred embodiments, thecircumferential sipes 30 are arranged to extend across the respectivefirst middle lateral grooves 21 but not to be communicated with thesecond middle lateral grooves 22. More specifically, the circumferentialsipes 30 extend across the respective circumferential groove portions 28of the first middle lateral grooves 21. Thus, at the groove bottoms ofthe circumferential groove portions 28, the circumferential sipes 30 areformed as the groove bottom sipes. On the other hand, the second middlelateral grooves 22 do not have such a structure. As a result, thesteering stability, on-snow performance, and uneven wear are resistancecan be improved in a well-balanced manner.

As illustrated in FIG. 2 , the first middle land portion 13 is furtherprovided with a plurality of first middle sipes 31 and a plurality ofsecond middle sipes 32. The first middle sipes 31 extend from the firstlongitudinal edge 13 a and are in communication with the respectivecircumferential sipes 30. The second middle sipes 32 extend from thesecond longitudinal edge 13 b and are in communication with therespective circumferential sipes 30. In some preferred embodiments,terminal ends 31 a of the first middle sipes 31 in the ground contactsurface 13 s are connected to ends on a first side in the tirecircumferential direction of the respective circumferential sipes 30.Terminal ends 32 a of the second middle sipes 32 in the ground contactsurface 13 s are connected to ends on a second side in the tirecircumferential direction of the respective circumferential sipes 30.The first middle sipes 31 and the second middle sipes 32 work togetherwith the circumferential sipe 30 to provide multi-directional frictionalforce, further improving on-snow performance.

The first middle sipes 31 and the second middle sipes 32, for example,are inclined with respect to the tire axial direction in the samedirection as the middle lateral grooves 20. An angle of these sipes withrespect to the tire axial direction, for example, ranges from 25 to 35degrees. In some preferred embodiments, an angle between the firstmiddle sipes 31 and the circumferential sipes 30 is an acute angle.Similarly, an angle between the second middle sipes 32 and thecircumferential sipes 30 is an acute angle. This makes it easier for thecorners between the middle sipes and the circumferential sipes to biteinto a road surface when driving on snow, thereby exhibiting excellentperformance on snow.

FIG. 8 illustrates a cross-sectional view taken along the line E-E ofFIG. 2 . FIG. 8 is a cross-sectional view of the first middle sipes 31,and the configuration described below can be applied to the secondmiddle sipes 32. As illustrated in FIG. 8 , the first middle sipes 31open at the ground contact surface 13 s via chamfer portions 35. Eachchamfer portion 35 includes an inclined surface 35 s between the groundcontact surface 13 s and one of the sipe walls 31 w. In the presentembodiment, each inclined surface 35 s is slightly curved in a directionconvex outward in the tire radial direction. The inclined surface 45 smay, for example, be planar. Such chamfer portions 35 help to equalizethe ground contact pressure acting on the ground contact surface 13 s,improving the steering stability and uneven wear resistance.

As illustrated in FIG. 2 , it is preferable that a chamfer width of thechamfer portions 35 of the first middle sipes 31 decreases toward thecircumferential sipe 30 side such that each first middle sipe 31 has anopening width at the ground contact surface 13 s which decreases towardthe terminal end 31 a of the first middle sipe 31. Similarly, it ispreferable that a chamfer width of the chamfer portions 35 of the secondmiddle sipes 32 decreases toward the circumferential sipe 30 side suchthat each second middle sipe 32 has an opening width at the groundcontact surface 13 s which decreases toward the terminal end 32 a of thesecond middle sipe 32. This ensures the ground contact area in a centerregion of the first middle land portion 13 and can maintain the steeringstability. The chamfer width is a width Wb in a direction orthogonal tothe longitudinal direction of the sipe (shown in FIG. 8 ) of the chamferportion in a tread plan view.

FIG. 9 illustrates an enlarged view of the crown land portion 15 of FIG.1 . The crown land portion 15 includes a first longitudinal edge 15 aextending in the tire circumferential direction on a first tread edge T1side, a second longitudinal edge 15 b extending in the tirecircumferential direction on a second tread edge T2 side, and a groundcontact surface 15 s between the first longitudinal edge 15 a and thesecond longitudinal edge 15 b. In addition, the crown land portion 15 isprovided with a plurality of first crown sipes 41, a plurality of secondcrown sipes 42, a plurality of third crown sipes 43, and a plurality offourth crown sipes 44.

FIG. 10 illustrates an enlarged view of one of the first crown sipes 41,one of the second crown sipes 42, one of the third crown sipes 43, andone of the fourth crown sipes 44. As illustrated in FIG. 10 , thesesipes are inclined at an angle with respect to the tire axial directionin the same direction with each other. In some preferred embodiments,these sipes are inclined in the same direction with respect to the tireaxial direction as with the middle lateral grooves 20 (shown in FIG. 2). An angle of these sipes, for example, ranges from 25 to 35 degreeswith respect to the tire axial direction.

The first crown sipes 41 extend from the first longitudinal edge 15 aand have closed ends 41 a in the ground contact surface 15 s. The secondcrown sipes 42 extend from the second longitudinal edge 15 b and haveclosed ends 42 a in the ground contact surface 15 s. The third crownsipes 43 extend from the first longitudinal edge 15 a and have closedends 43 a in the ground contact surface 15 s. In a tread plan view, thethird crown sipes 43 have a shape different from the first crown sipes41. The fourth crown sipes 44 extend from the second longitudinal edge15 b and have closed ends 44 a in the ground contact surface 15 s. In atread plan view, the fourth crown sipes 44 have a shape different fromthe second crown sipes 42.

In the present embodiment, a minimum distance L4 in the tirecircumferential direction between outer ends 41 b on the firstlongitudinal edge 15 a side of the first crown sipes 41 and outer ends42 b on the second longitudinal edge 15 b side of the second crown sipes42 is preferably equal to or less than 10% of a circumferentialarrangement pitch P1 (shown in FIG. 9 ) of the first crown sipes 41.This makes it easier for water pushed away by a middle region of thecrown land portion 15 to be guided to the outer edges of these sipeswhen driving on wet roads, thus improving wet performance.

A length L6 in the tire axial direction of the first crown sipes 41, forexample, ranges from 40% to 60% of a width W5 (shown in FIG. 9 ) in thetire axial direction of the ground contact surface 15 s of the crownland portion 15. Note that in this document, a length of a sipe ismeasured by the center line of the sipe.

Preferably, the second crown sipes 42 extend beyond the axial center inthe tire axial direction of the ground contact surface 15 s of the crownland portion 15. The closed ends 42 a of the second crown sipes 42 arelocated on the first longitudinal edge 15 a side with respect to theclosed ends 41 a of the first crown sipes 41. Preferably, a length L7 inthe tire axial direction of the second crown sipes 42 is greater thanthe length L6 in the tire axial direction of the first crown sipes 41.Specifically, the length L7 of the second crown sipes 42 preferablyranges from 65% to 85% of the width W5 in the tire axial direction ofthe ground contact surface 15 s of the crown land portion 15. The secondcrown sipes 42 as such can improve on-snow performance and wetperformance while maintaining steering stability.

Preferably, a minimum distance L5 in the tire circumferential directionbetween outer ends 43 b on the first longitudinal edge 15 a side of thethird crown sipes 43 and outer ends 44 b on the second longitudinal edge15 b side of the fourth crown sipes 44 is equal to or less than 10% of acircumferential arrangement pitch P2 (shown in FIG. 9 ) of the thirdcrown sipes 43. This can improve wet performance further.

A length L8 in the tire axial direction of the third crown sipes 43 issmaller than the length L7 of the second crown sipes 42 and the lengthL6 of the first crown sipes 41. In addition, the closed ends 43 a of thethird crown sipes 43 are located on the first longitudinal edge 15 aside with respect to the closed ends 44 a of the fourth crown sipes 44.In some more preferred embodiments, the closed ends 43 a of the thirdcrown sipes 43 are located on the second longitudinal edge 15 b sidewith respect to the closed ends 42 a of the second crown sipes 42. Thelength L8 of the third crown sipes 43 ranges from 25% to 45% of thewidth W5 of the ground contact surface 15 s of the crown land portion15. Such third crown sipes 43 can help to improve steering stability,on-snow performance, and wet performance in a well-balanced manner.

From a similar point of view, a length L9 in the tire axial direction ofthe fourth crown sipes 44, for example, is smaller than the length L7 ofthe second crown sipes 42 and the length L6 of the first crown sipes 41.Specifically, the length L9 of the fourth crown sipes 44 preferablyrange from 25% to 45% of the width W5 of the ground contact surface 15 sof the crown land portion 15.

The first crown sipes 41, the second crown sipes 42, the third crownsipes 43, and the fourth sipes 44 open at the ground contact surface 15s via chamfer portions 45. Such a structure can equalize the groundpressure acting on the ground contact surface 15 s of the crown landportion 15, thereby improving steering stability and uneven wearresistance. Note that the configuration of the chamfer portions 35 ofthe first middle sipes 31 (shown in FIG. 8 ) can be applied to thechamfer portions 45 of these sipes, which will not be explained herein.

As illustrated in FIG. 9 , the first crown sipes 41 and the second crownsipes 42 preferably open at the ground contact surface via the chamferportions 45 over the entire length thereof. In addition, an openingwidth W6 at the ground contact surface 15 s of each of the first crownsipes 41 is preferably constant in the longitudinal direction of thesipe, and an opening width W7 at the ground contact surface 15 s of eachof the second crown sipes 42 is preferably constant in the longitudinaldirection of the sipe. Preferably, the opening width W7 of each of thesecond crown sipes 42 ranges from 80% to 120% of the opening width W6 ofeach of the first crown sipes 41, and in this embodiment, they aresubstantially the same with each other. Thus, uneven wear around thesipes can be suppressed.

Preferably, an opening width at the ground contact surface 15 s of eachof the third crown sipes 43 decreases continuously from the firstlongitudinal edge 15 a toward the closed end 43 a. Preferably, anopening width at the ground contact surface 15 s of each of the fourthcrown sipes 44 decreases continuously from the second longitudinal edge15 b toward the closed end 44 a. This ensures sufficient ground contactarea in a center region of the crown land portion 15, maintaining bettersteering stability. In the third crown sipes 43 of the presentembodiment, each chamfer portion is substantially eliminated at theclosed end 43 a, but each chamfer portion 45 is not limited to such anaspect, and one or more chamfer portions 45 may have a chamfer width atthe closed ends 43 a. The same is true for the fourth crown sipes 44.

The maximum opening width W8 at the ground contact surface 15 s of eachof the third crown sipes 43 is smaller than the opening width W6 at theground contact surface 15 s of each of the first crown sipes 41.Specifically, the maximum opening width W8 of each of the third crownsipes 43 ranges from 75% to 90% of the opening width W6 of each of thefirst crown sipes 41. Similarly, the maximum opening width W9 at theground contact surface 15 s of each of the fourth crown sipes 44 issmaller than the opening width W7 of each of the second crown sipes 42.Specifically, the opening width W9 of the fourth crown sipes 44 rangesfrom 75% to 90% of the opening width W7 of the second crown sipes 42.The third crown sipes 43 and the fourth crown sipes 44 can help toenhance the balance between steering stability and on-snow performance.

FIG. 11 illustrates an enlarged view of the second middle land portion14. As illustrated in FIG. 11 , the second middle land portion 14 isprovided with third middle lateral grooves 23 and fourth middle lateralgrooves 24 which are arranged alternately in the tire circumferentialdirection. The third middle lateral grooves 23 and the fourth middlelateral grooves 24 have the same shape in a tread plan view, and extendacross the second middle land portion 14 entirely in the tire axialdirection. In addition, the third middle lateral grooves 23 and thefourth middle lateral grooves 24 are inclined with respect to the tireaxial direction in the same direction as the middle lateral grooves 20(shown in FIG. 2 ). An angle of the third middle lateral grooves 23 andthe fourth middle lateral grooves 24 with respect to the tire axialdirection is smaller than an angle of the middle lateral grooves 20(shown in FIG. 2 ) with respect to the tire axial direction and an angleof the sipes provided on the crown land portion 15 (shown in FIG. 9 )with respect to the tire axial direction. Specifically, an angle of thethird middle lateral grooves 23 and the fourth middle lateral grooves 24with respect to the tire axial direction, for example, ranges from 10 to20 degrees. On the other hand, the third middle lateral grooves 23 andthe fourth middle lateral grooves 24 differ in groove bottom structure.

FIG. 12 illustrates a cross-sectional view taken along the line F-F ofFIG. 11 . As illustrated in FIG. 12 , the third middle lateral grooves23 each have a shallow groove portion 46 on the second crowncircumferential groove 8 side and a deep groove portion 47 on the secondshoulder circumferential groove 6 side. FIG. 13 illustrates across-sectional view taken along the line G-G of FIG. 11 . Asillustrated in FIG. 13 , the fourth middle lateral groove 24 havesubstantially the inverted shape of the third middle lateral grooves 23.That is, the fourth middle lateral grooves 24 each have a deep grooveportion 47 on the second crown circumferential groove 8 side and ashallow groove portion 46 on the second shoulder circumferential groove6 side. In this embodiment, the third middle lateral grooves 23 and thefourth middle lateral grooves 24 are provided alternately in the tirecircumferential direction, which improve the uneven wear resistance andthe steering stability.

For the shallow groove portions 46 of the third middle lateral grooves23 and the fourth middle lateral grooves 24, the shallow groove portions36 of the middle lateral grooves 20 (shown in FIG. 7 ) of the middlelateral grooves 20 described above can be applied to the shallow grooveportions 46 of the third middle lateral grooves 23 and the fourth middlelateral grooves 24. Similarly, for the deep groove portions 47 of thethird middle lateral grooves 23 and the fourth middle lateral grooves24, the deep groove portions 37 of the middle lateral grooves 20 (shownin FIG. 6 ) of the middle lateral grooves 20 described above can beapplied to the deep groove portions 47 of the third middle lateralgrooves 23 and the fourth middle lateral grooves 24.

As illustrated in FIG. 11 , the second middle land portion 14 isprovided with a plurality of middle sipe groups 55 each of whichincludes a plurality of bent sipes 56 arranged in the tire axialdirection. The middle sipe groups 55 are spaced in the tirecircumferential direction. In the present embodiment, each middle sipegroup 55 is configured such that the plurality of bent sipes 56 isarranged so as to overlap partially in the tire axial direction witheach other. The bent sipes 56 each include a convex part on one side orthe other in the tire circumferential direction. The middle sipe groups55 are difficult to open during braking and driving, so that snow andice are less likely to clog the inside of the sipes, and thus excellenton-snow performance can be maintained.

The present disclosure is not limited to the second middle land portion14 shown in FIG. 11 . FIG. 14 illustrates an enlarged view of the secondmiddle land portion 14 in accordance with another embodiment of thepresent disclosure. As illustrated in FIG. 14 , the second middle landportion 14 according to this embodiment is provided with a plurality ofthird middle sipes 33 and a plurality of fourth middle sipes 34, inaddition to the third middle lateral grooves 23 and the fourth middlelateral grooves 24 described above. The third middle sipes 33 extendfrom the second crown circumferential groove 8 and are terminated in theground contact surface of the second middle land portion 14. The fourthmiddle sipes 34 extend from the second shoulder circumferential groove 6and are terminated in the ground contact surface. The third middle sipes33 and the fourth middle sipes 34 are inclined, for example, in the samedirection as the third middle lateral grooves 23 and the fourth middlelateral grooves 24 with respect to the tire axial direction. An angle ofthese sipes with respect to the tire axial direction ranges, forexample, from 10 to 20 degrees. For the third middle sipes 33 and thefourth middle sipes 34, the configuration of the first middle sipes 31or the second middle sipes 32 described above can be applied.

In yet another embodiment of the second middle land portion 14, forexample, between the adjacent third and fourth middle lateral grooves 23and 24 in the tire circumferential direction, one or more middle sipegroups 55 described above (shown in FIG. 11 ) and one or more third andfourth middle sipes 33 and 34 shown in FIG. 14 may be arranged (notshown). Such an arrangement of the sipes can help to further enhanceon-snow performance.

As illustrated in FIG. 1 , the first shoulder land portion 11 isprovided with a plurality of first shoulder lateral grooves 51 and aplurality of first shoulder sipes 52. The first shoulder lateral grooves51 and the first shoulder sipes 52 extend, for example, from the firstshoulder circumferential groove 5 to at least the first tread edge T1.In addition, the second shoulder land portion 12 is provided with aplurality of second shoulder lateral grooves 53 and a plurality ofshoulder sipe groups 60 each of which includes a plurality of bent sipes61 arranged in the tire axial direction. The shoulder sipe groups 60have substantially the same configuration as the middle sipe groups 55described above. These grooves and sipes can help to further improveon-snow performance.

Although the tire according to one or more embodiments of the presentdisclosure has been described in detail above, the present disclosure isnot limited to the specific embodiments described above, and can beembodied in various ways.

EXAMPLE

Pneumatic tires of size 245/40ZR18 having the basic pattern shown inFIG. 1 were prepared. Also, as Comparative example, pneumatic tires wereprepared in which the first middle land portion has a plurality ofmiddle lateral grooves extending at an angle with respect to the tireaxial direction with a constant groove width without including thecircumferential groove portions (not shown). The middle lateral groovesof Comparative example extend in the tire axial direction with aconstant groove depth. Further, the groove depth of each middle lateralgroove of the comparative example is determined so that the groovevolume is substantially the same as the groove volume of each middlelateral grooves of Example. Furthermore, except for the above-mentioneditems, Example and the comparative example have substantially the sameconfiguration. Then, steering stability on dry roads and on-snowperformance were tested for Example and Comparative examples. Commonspecifications and test methods for each test tire are as follows.

-   -   Rim size: 18×8.5 J    -   Tire pressure: 240 kPa for all wheels    -   Test vehicle: 2000 cc displacement, rear wheel drive    -   Tire mounting location: All wheels

Steering Stability on Dry Road Test:

The steering stability when the test vehicle was driven on a dry roadsurface was evaluated by the senses of the driver. The test results areindicated in Table 1 using a score with the steering stability ofComparative example being 100, and the larger the number, the better thesteering stability.

On-Snow Performance Test:

When the above test vehicle was driven on snow, the performance on snowwas evaluated by the senses of the driver. The test results areindicated in table 1 using a score with the on-snow performance ofComparative example being 100, and the larger the number, the better theon-snow performance.

Table 1 shows the test results.

TABLE 1 Comparative example Example Steering stability on dry roads(score) 100 100 On-snow performance (score) 100 105

As a result of the test, it is confirmed that the tire of Exampleexhibits excellent on-snow performance while maintaining steeringstability on dry roads.

Additional Notes

The present disclosure includes the following aspects.

[Note 1]

A tire comprising:

-   -   a tread portion comprising a first tread edge, a second tread        edge, a first middle land portion arranged between the first        tread edge and the second tread edge, wherein    -   the first middle land portion comprises a first longitudinal        edge extending in a tire circumferential direction on a first        tread edge side, a second longitudinal edge extending in the        tire circumferential direction on a second tread edge side, and        a ground contact surface between the first longitudinal edge and        the second longitudinal edge,    -   the first middle land portion is provided with a plurality of        middle lateral grooves that traverses the first middle land        portion completely in a tire axial direction,    -   at least one of the plurality of middle lateral grooves        comprises a first groove portion extending in the tire axial        direction from the first longitudinal edge, and a second groove        portion extending in the tire axial direction from the second        longitudinal edge,    -   the first groove portion and the second groove portion are        offset in the tire circumferential direction to form a pair of        circumferential groove edges extending in the tire        circumferential direction between a pair of groove edges of the        first groove portion and a pair of groove edges of the second        groove portion, and    -   a maximum groove depth of the first groove portion is different        from a maximum groove depth of the second groove portion.

[Note 2]

The tire according to note 1, wherein

-   -   each of the plurality of middle lateral grooves comprises the        first groove portion and the second groove portion,    -   the plurality of middle lateral grooves comprises a plurality of        first middle lateral grooves and a plurality of second middle        lateral grooves,    -   each of the plurality of first middle lateral grooves comprises        the first groove portion having a maximum groove depth smaller        than a maximum groove depth of the second groove portion,    -   each of the plurality of second middle lateral grooves comprises        the first groove portion having a maximum groove depth greater        than a maximum groove depth of the second groove portion, and    -   the plurality of first middle lateral grooves and the plurality        of second middle lateral grooves are arranged alternately in the        tire circumferential direction.

[Note 3]

The tire according to note 1 or 2, wherein

-   -   a length in the tire circumferential direction of the pair of        circumferential groove edges is smaller than the maximum groove        width of the first groove portion and the maximum groove depth        of the second groove portion.

[Note 4]

The tire according to any one of notes 1 to 3, wherein

-   -   the at least one of the plurality of middle lateral grooves        comprises a circumferential groove portion arranged between the        first groove portion and the second groove portion, and    -   a maximum groove depth of the circumferential groove portion is        smaller than the maximum groove depth of the first groove        portion and the maximum groove depth of the second groove        portion.

[Note 5]

The tire according to any one of notes 1 to 4, wherein

-   -   the first middle land portion is further provided with at least        one circumferential sipe extending across the at least one of        the plurality of middle lateral grooves in the tire        circumferential direction.

[Note 6]

The tire according to note 5, wherein

-   -   the first middle land portion is further provided with at least        one first middle sipe extending from the first longitudinal edge        and being in communication with the at least one circumferential        sipe.

[Note 7]

The tire according to note 5 or 6, wherein

-   -   the first middle land portion is further provided with at least        one second middle sipe extending from the second longitudinal        edge and being in communication with the at least one        circumferential sipe.

[Note 8]

The tire according to any one of notes 1 to 7, wherein

-   -   the tread portion has a designated mounting direction on a        vehicle, and    -   the first tread edge is located outside the vehicle when mounted        on the vehicle.

1. A tire comprising: a tread portion comprising a first tread edge, asecond tread edge, a first middle land portion arranged between thefirst tread edge and the second tread edge, wherein the first middleland portion comprises a first longitudinal edge extending in a tirecircumferential direction on a first tread edge side, a secondlongitudinal edge extending in the tire circumferential direction on asecond tread edge side, and a ground contact surface between the firstlongitudinal edge and the second longitudinal edge, the first middleland portion is provided with a plurality of middle lateral grooves thattraverses the first middle land portion completely in a tire axialdirection, at least one of the plurality of middle lateral groovescomprises a first groove portion extending in the tire axial directionfrom the first longitudinal edge, and a second groove portion extendingin the tire axial direction from the second longitudinal edge, the firstgroove portion and the second groove portion are offset in the tirecircumferential direction to form a pair of circumferential groove edgesextending in the tire circumferential direction between a pair of grooveedges of the first groove portion and a pair of groove edges of thesecond groove portion, and a maximum groove depth of the first grooveportion is different from a maximum groove depth of the second grooveportion.
 2. The tire according to claim 1, wherein each of the pluralityof middle lateral grooves comprises the first groove portion and thesecond groove portion, the plurality of middle lateral grooves comprisesa plurality of first middle lateral grooves and a plurality of secondmiddle lateral grooves, each of the plurality of first middle lateralgrooves comprises the first groove portion having a maximum groove depthsmaller than a maximum groove depth of the second groove portion, eachof the plurality of second middle lateral grooves comprises the firstgroove portion having a maximum groove depth greater than a maximumgroove depth of the second groove portion, and the plurality of firstmiddle lateral grooves and the plurality of second middle lateralgrooves are arranged alternately in the tire circumferential direction.3. The tire according to claim 1, wherein a length in the tirecircumferential direction of the pair of circumferential groove edges issmaller than the maximum groove width of the first groove portion andthe maximum groove depth of the second groove portion.
 4. The tireaccording to claim 1, wherein the at least one of the plurality ofmiddle lateral grooves comprises a circumferential groove portionarranged between the first groove portion and the second groove portion,and a maximum groove depth of the circumferential groove portion issmaller than the maximum groove depth of the first groove portion andthe maximum groove depth of the second groove portion.
 5. The tireaccording to claim 1, wherein the first middle land portion is furtherprovided with at least one circumferential sipe extending across the atleast one of the plurality of middle lateral grooves in the tirecircumferential direction.
 6. The tire according to claim 5, wherein thefirst middle land portion is further provided with at least one firstmiddle sipe extending from the first longitudinal edge and being incommunication with the at least one circumferential sipe.
 7. The tireaccording to claim 5, wherein the first middle land portion is furtherprovided with at least one second middle sipe extending from the secondlongitudinal edge and being in communication with the at least onecircumferential sipe.
 8. The tire according to claim 1, wherein thetread portion has a designated mounting direction on a vehicle, and thefirst tread edge is located outside the vehicle when mounted on thevehicle.
 9. The tire according to claim 5, wherein the first middle landportion is further provided with at least one first middle sipeextending from the first longitudinal edge and being in communicationwith a first end of at least one circumferential sipe, and at least onesecond middle sipe extending from the second longitudinal edge and beingin communication with a second end of the at least one circumferentialsipe.
 10. The tire according to claim 9, wherein the at least one firstmiddle sipe extends straight over an entire length thereof, and the atleast one second middle sipe extends straight over an entire lengththereof.
 11. The tire according to claim 10, wherein the at least onefirst middle sipe is inclined with respect to the tire axial directionin a same direction as the at least one second middle sipe.
 12. The tireaccording to claim 11, wherein the at least one first middle sipeextends in parallel with the at least one second middle sipe.
 13. Thetire according to claim 9, wherein the at least one circumferential sipeextends straight, and the at least one circumferential sipe is inclinedwith respect to the pair of groove edges of the first groove portion.14. The tire according to claim 13, wherein the first groove portion hasan opening width in the ground contact surface, and the opening width ofthe first groove portion decreases from the first longitudinal edgetoward the at least one circumferential sipe.
 15. The tire according toclaim 14, wherein the second groove portion has an opening width in theground contact surface, and the opening width of the second grooveportion decreases from the second longitudinal edge toward the at leastone circumferential sipe.
 16. The tire according to claim 1, wherein anangle of the pair of circumferential groove edges is equal to or lessthan 10 degrees with respect to the tire circumferential direction. 17.The tire according to claim 13, wherein an angle of the pair ofcircumferential groove edges is equal to or less than 10 degrees withrespect to the tire circumferential direction.
 18. The tire according toclaim 1, wherein the pair of circumferential groove edges extend inparallel with the tire circumferential direction.
 19. The tire accordingto claim 13, wherein the pair of circumferential groove edges extend inparallel with the tire circumferential direction.
 20. The tire accordingto claim 1, wherein the pair of circumferential groove edges is locatedentirely in a central area when the ground contact surface of the firstmiddle land portion is divided into three equal portions in the tireaxial direction.